Here is the definition of Thanksgiving Day from the Encyclopedia Britannica 11th edition from 1911.

THANKSGIVING DAY, in the United States, the fourth Thursday in November, annually set apart for thanksgiving by proclamation of the president and of the governors of the various states. The day is observed with religious services in the churches, and, especially in New England, as an occasion for family reunion.Encyclopedia Britannica 11th edition, 1911

Another definition from the American Heritage Dictionary.

Thanksgiving Day
1. The fourth Thursday of November, observed as a legal holiday in the United States to commemorate the feast held at Plymouth in 1621 by the Pilgrim colonists and members of the Wampanoag people and marked by the giving of thanks to God for harvest and health.American Heritage Dictionary

The exact definition of what Thanksgiving Day is is not perfectly consistent. Another reference defines the day with some significant differences.

Thanksgiving Day, legal holiday observed annually in the United States on the fourth Thursday of November. In Canada, Thanksgiving falls on the second Monday in October. Its origin probably traces to harvest festivals that have been traditional in many parts of the world since ancient times (see Festivals and Feasts). Today Thanksgiving is mainly a celebration of domestic life, centered on the home and family. Most people celebrate Thanksgiving by gathering with family or friends for a holiday feast.Microsoft ® Encarta ® 2006

Which definition is accurate? Is Thanksgiving a commemoration of the Pilgrims 1621 feast, a day of religious services and family reunions or a harvest festival that celebrates domestic life? Or is it all of the above? Is it secular or religious? Thanksgiving appears to have an identity crisis similar to Christmas and Easter. Does the the word “thanksgiving” in “Thanksgiving Day” mean the same thing as the English word “thanksgiving”? Here is the definition of the word thanksgiving.

thanks·giv·ing (plural thanks·giv·ings) noun
1. prayer of thanks: a prayer that offers thanks to God
2. giving of thanks: an expression or an act of giving thanks
3. public acknowledgment of divine goodness: a public acknowledgment or celebration of divine goodnessMicrosoft® Encarta® 2006

The acts during the observance of Thanksgiving Day do not fit the description of what thanksgiving means. Two of the three definitions of thanksgiving are purely religious. Which of these definitions accurately describes our actions and activities on Thanksgiving Day? Does the name alone define what it is?

If Thanksgiving Day were to be renamed would it still be the same day? What if it was called Turkey Day, Harvest Home, Lammas Day, Erntedank or Sukkot? Would it still be the same festival?

All references above agree (after 1941) that part of the definition of Thanksgiving Day is one of a “legal holiday”. But is Thanksgiving day more similar to the Fourth of July and Memorial Day or Christmas and Easter? Note the difference in the definitions of Christmas and Easter compared to Thanksgiving.

Easter, annual festival commemorating the resurrection of Jesus Christ, and the most important feast of the Christian year.Microsoft ® Encarta ® 2006

Are Christmas and Easter more religious days than Thanksgiving? Here's where the confusion on Thanksgiving Day starts.

The occasion [the first thanksgiving] had hardly enough of a religious character to satisfy our modern ideas of propriety.Our New England Thanksgiving, Historically Considered, Rev. I. N. Tarbox, D.D 1879

Are the “traditional” roots of thanksgiving a religious event or a secular one? Does Thanksgiving come from the non-religious 1621 harvest festival or the myriad of other well documented religious thanksgivings? Is it even possible for Thanksgiving to have both secular and religious roots?